One of the charms of Petersburg is that it doesn't have a deep water port, so it's not accessible by big cruise ships, but some smaller ships stop there. The Alaska Marine Highway provides regular ferry service.
There is a local taxi and some local shuttle services. The local roads are also nice for bicycling, although the size of the island limits the overall distance one can travel. Rental cars are available from both the hotels in town. Boats can even be rented from the Scandia House.
Le Conte Glacier. the southernmost tidewater glacier in the northern hemisphere. The glacier moves extremely quickly, offering almost continual calving, including underwater calving leading to "shooters" as icebergs rise rapidly to the surface from the hundreds of feet of submerged ice. Hundreds of harbor seals also inhabit the fjord created by the glacier; closer to the face you're likely to see them lolling about on icebergs. edit
Whale watching - as Petersburg is located on the south end of Frederick Sound, where many humpback whales summer, it is an ideal starting point for whale watching. Although it's less comfortable to be out on the sound during rougher weather, days with lots of waves are better for seeing aerial displays.
Clausen Memorial Museum has local history exhibits.
Sons of Norway Hall, Sing Lee Alley. Built in 1910, the Sons of Norway Hall is a registered historic landmark and continues to be at the center of many local social events, from weddings to dances to public meetings. edit
Blind River Rapids, mile 14.2 on Mitkof Highway  A boardwalk through the muskeg to Blind Slough, where the salmon are numerous and other wildlife is often visible.
Sea Kayaking Wilderness kayak camping tours to Petersburg Creek, Frederick Sound to view humpback whales and other marine wildlife, and to the LeConte Glacier to paddle among the icebergs. Tour lengths of four hours to several days available. 360-378-5767 or 888-589-4253, firstname.lastname@example.org Sea Kayaking Tours from Petersburg, Alaska
Behind the school there's a boardwalk through the muskeg (extremely soft nutrient poor meadow) that's worth walking.
Tongass Kayak Adventures, ☎ 772-4600, . Tongass Kayak offers four-hour to multi-day kayak trips throughout the area. Kayak trips to LeConte Glacier Bay and whale watching are favorites as is a day trip into the Petersburg Creek Wilderness area. edit
Because Petersburg doesn't have a deep water port, it doesn't get the large cruise ships; thus, it isn't overrun with the large cruise line operated tourist shops that plague many such coastal towns. There are a few little locally owned galleries with local artists, and a bookstore with some nice coffee table books, but most of the town actually exists for the local population.
Lee's Clothing, Main Street. M-S. Lee's is a family owned business offering great outdoor clothes and a fine selection of Norwegian sweaters.edit
Sing Lee Alley Books, 11 Sing Lee Alley, ☎ 907 772-4440. As mentioned above, Sing Lee Alley Books has an "Alaska Room" with a good assortment of Alaskana including field guides and history, but you can also find new releases and good selection of fiction to keep you happy during your trip. edit
There are two bars open to the public. Harbor Bar is located on main street and Kito's Kave is a short distance away on Sing Lee Alley. There are Moose and Elk's lodges for members as well. All establishments are smoke-free as of 2010.
Scandia House The newer hotel. Has a jacuzzi suite available. Located in the center of downtown. Has a coffee shop on the first floor.
Tides Inn Also located close to the center of town.
Morning Mist Bed and Breakfast - Mel and Sherry Stockton are the great hosts.
Water's Edge Bed and Breakfast - the delightful host Barry is a very friendly person.
Sea Level B&B, North Nordic Drive, ☎ 907-772-3240, . This B&B has an incredible location and views. It sits out over the water so you can see whales and seals from your room. Also has a great view of the coastal mountain range. Close enough to downtown that you can walk.edit
"the Lucky Loon" http://www.theluckyloon.com A furnished house on the shores of Frederick Sound with incredible views. Five day minimum rental that books a year in advance for the summer months. Whales and other marine life are often sighted from the living room and deck.